Diego Nicola Barbato <dnbarbato@posteo.de> writes:

> Apparently this was a known bug in ImageMagick 6.9.9-15 (and 6.9.9-17)
> (https://github.com/ImageMagick/ImageMagick/issues/825). It has been
> fixed in version 6.9.9-18.

Hello!  I just pushed an update to 6.9.9-18, can you verify that it
works?

Thanks for the report!